Ruby Bindings for pfio.c

The pfio C Library is used to control the Pi-Face Digital Interface for Raspberry Pi. This gem uses the Ruby-FFI gem to bind the C functions to ruby.

!! Project is currently in ALPHA (Things may change)

Ruby method names, as well as other aspects, may change until version 1.0 is released.

Basic Usage

The PiFace has 8 inputs and 8 outputs. Both the inputs and outputs are linked to connectors 1-8 respectfully.

Note: The pfio C library will set all outputs to LOW (zero) when first initialized.

Using Outputs

Writing to outputs 1 to 8 with all turn on the LEDs. Write to outputs using Piface::LOW (or 0) for off/disable and Piface::HIGH (or 1) for on/enable.

Please note that the PiFace outputs are all open-collectors (meaning that they do not output any voltage). Please read the PiFace Manual for more information.

require 'piface'

# Enable output 4
Piface.write 4, 1

sleep 1 # wait one second

# Disable output 4
Piface.write 4, 0

Using Relays

Write to outputs 1 and 2 to control the relays (if jumpers JP5 and JP6 are enabled on the PiFace).

require 'piface'

# Turn on the first relay
Piface.write 1, 1

sleep 1 # wait one second

# Turn off first relay
Piface.write 1, 0

Using Classes

Sometimes it's nice to represent an output using a class. One common example is when you want to track the current state of the output.

require 'piface'

# Relay class implementing toggle functionality
class Relay
  def initialize(relay_number)
    @relay_number = relay_number
    @state = 0
  end

  def turn_on
    Piface.write @relay_number, 1
    @state = 1
  end

  def turn_off
    Piface.write @relay_number, 0
    @state = 0
  end

  def toggle
    @state == 1 ? turn_off : turn_on
  end
end

relay1 = Relay.new(1)

# Turn the relay on and off 3 times
6.times do
  relay1.toggle
  sleep 1 # wait one second
end

Using Inputs

The PiFace uses digital inputs. Reading the value with return either a 0 or 1. Since the PiFace uses pull-up resistors for inputs, by default they will read 1. This means to check for input (such as button presses), you must compare the read input value with 0 for on.

require 'piface'

# Read value from input 6 (without active input)
Piface.read 6
# => 1

# Read value from input 6 (with active input)
Piface.read 6
# => 0

Using Buttons

The PiFace has 4 built-in buttons that correspond to inputs 1 to 4.

require 'piface'

# Listen for button 4 press
loop do
  # Check if the button has been pressed
  if (Piface.read(4) == Piface::LOW)
    puts "Button 4 pressed"
  end
  sleep 0.1 # sleep to be kind to the CPU
end

Additional Resources

Installation

First install the pfio C Library

https://github.com/thomasmacpherson/piface

Enable RaspberryPi's SPI module

$ gpio load spi

Add this line to your application's Gemfile:

gem 'piface'

And then execute:

$ bundle

Or install it yourself as:

$ gem install piface

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Added some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request